The calcium ion concentration in serum is determined using an ion-selective electrode. The potential measured with the electrode in the sample is +217.6 mV. Addition of 100 µL of a 2000ppm standard to 2.00 mL of sample and measurement of the potential gives +226.8 mV. Assuminga Nernstian response (β = 1), what is the concentration of calcium ion in the sample?